In recent years, cancer has surpassed heart disease as the leading cause of death among Americans who are younger than 85 years. In particular, breast cancer is the second leading cause of cancer-related deaths in the United States and often leads to secondary metastatic tumor sites in the bone, lungs, and liver. Tumor progression and metastasis involve two basic cellular processes: cell migration through interstitial tissues and cell division at the primary tumor and distal metastatic sites. During these processes, cells are subjected to complex three-dimensional environments that vary both biologically and physically. In this proposal, the overall objective is to evaluate how cell volume and polarity are regulated during migration and division when cells are subjected to varying degrees of physical confinement and/or matrix elasticity. We will use a combination of microfabricated devices, cell engineering techniques, and high-resolution phase contrast and laser scanning confocal timelapse microscopy to accomplish this objective. We hypothesize that the physical properties of the breast cancer cell microenvironment regulate cell volume and polarity during migration and the cell cycle. Two specific aims are proposed to address this hypothesis: (1) Elucidate the molecular mechanisms of cell migration and volume regulation in response to osmotic shock in confined microenvironments; and (2) Evaluate the effects of confinement and microenvironment elasticity on the spatial and temporal regulation of the cell cycle. The long-term goals of this project are to (1) contribute to our understanding of how cell volume and polarity are regulated during migration and division in confined microenvironments on a basic science level; (2) provide knowledge that could ultimately be used in the development of novel treatment strategies to control breast cancer cell proliferation and metastasis, (3) provide me with experimental and theoretical training in the field of cancer biophysics, which will be necessary for my future career as an independent researcher; and (4) contribute to my career development, through training on grant and manuscript writing, mentoring of graduate and undergraduate students, public speaking, and networking with future collaborators. Activities planned under the fellowship include original research (60% of time); manuscript preparation (10%); grant writing (10%); formal course work on Cancer Biology, Research Leadership, and Responsible Conduct of Research (5%); attendance at professional meetings (5%); participation in laboratory group meetings of our lab and collaborators (5%); mentoring Ph.D. and undergraduate students (2%); attendance at departmental seminars (2%); and participation in a postdoctoral journal club (1%). In completing the activities proposed under this fellowship, I will be prepared to begin an independent faculty career and will have the knowledge base and skill set to address biological problems relating to cancer using bioengineering strategies. !